This invention generally relates to coating systems for protecting metal substrates. More specifically, the invention is directed to a thermal barrier coating with improved overall thermal insulation characteristics.
Thermal barrier coatings (TBC) are used on gas turbine engine components such as buckets, nozzles, shrouds. A typical TBC is expected to protect substrate materials against hostile corrosion and oxidation environments found in gas turbine engines. The thermal conductivity properties of at least some known ceramic TBC are an order of magnitude lower than typical nickel-based and cobalt-based superalloys. The thickness of TBC can be tailored to achieve a desired level of thermal resistance, i.e. required temperature drop across a TBC system. Therefore, a TBC forms a thermal barrier to heat flow, reducing a cooling requirement to the substrate and increasing thermal efficiency. Additionally, the TBC can be used to enhance durability of substrate by decreasing operating temperature, which may decrease susceptibility to creep and low cycle fatigue (LCF) failures in coated components.
The application of TBC on modern gas turbine components includes a coating of predetermined thickness to achieve a desired thermal insulation. Thermal insulation is a function of the TBC thickness and the TBC conductivity. The lower the thermal conductivity, the higher is the insulation capability of a TBC of specified thickness. Therefore, by decreasing conductivity of conventional TBCs, it is possible to achieve higher thermal insulation to gas turbine components. A reduced amount of coating thickness by decreasing conductivity of the TBC provides manufacturing cost savings.